NAME

       gl_Position - contains the position of the current vertex

DECLARATION

       gl_Position is a member of the gl_PerVertex named block:

           out gl_PerVertex {
               vec4 gl_Position;
               float gl_PointSize;
               float gl_ClipDistance[];
           };

DESCRIPTION

       In the vertex, tessellation evaluation and geometry languages, a single global instance of
       the gl_PerVertex named block is available and its gl_Position member is an output that
       receives the homogeneous vertex position. It may be written at any time during shader
       execution. The value written to gl_Position will be used by primitive assembly, clipping,
       culling and other fixed functionality operations, if present, that operate on primitives
       after vertex processing has occurred.

       In the tessellation control language, the gl_PerVertex named block is used to construct an
       array, gl_out[], whose gl_Position members hold the homogeneous control point position,
       which become available as inputs to the subsequent tessellation evaluation shader.

       The value of gl_Position (or the gl_Position member of the gl_out[] array, in the case of
       the tessellation control shader) is undefined after the vertex, tessellation control, and
       tessellation evaluation shading stages if the corresponding shader executable does not
       write to gl_Position. It is also undefined after the geometry processing stage if the
       geometry shader executable calls EmitVertex() without having written gl_Position since the
       last call to EmitVertex() (or hasn't written it at all).

       In the tessellation control, tessellation evaluation and geometry languages, the
       gl_PerVertex named block is used to construct an array, gl_in[] of per-vertex or
       per-control point inputs whose content represents the corresponding outputs written by the
       previous stage.

VERSION SUPPORT

       ┌────────────┬───────────────────────────────────────────────────────────────────────────────────┐
       │            │        OpenGL Shading Language Version                                            │
       ├────────────┼──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┤
       │Function    │ 1.10 │ 1.20 │ 1.30 │ 1.40 │ 1.50 │ 3.30 │ 4.00 │ 4.10 │ 4.20 │ 4.30 │ 4.40 │ 4.50 │
       │Name        │      │      │      │      │      │      │      │      │      │      │      │      │
       ├────────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┤
       │gl_Position │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │
       └────────────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┘
       Versions 1.10 to 1.40 - vertex shader only.

       Versions 1.50 to 3.30 - vertex and geometry shaders only.

SEE ALSO

       gl_PointSize(), gl_ClipDistance()

COPYRIGHT

       Copyright © 2011-2014 Khronos Group. This material may be distributed subject to the terms
       and conditions set forth in the Open Publication License, v 1.0, 8 June 1999.
       http://opencontent.org/openpub/.

COPYRIGHT

       Copyright © 2011-2014 Khronos Group

[FIXME: source]                             07/22/2015                            GL_POSITION(3G)